High-temperature getters for electronic tubes



May 22, 1956 l. E. LEVY 2,747,124

HIGH-TEMPEATURE GETTERS FOR ELECTRONIC TUBES Filed Sept. 17, 1953 Ziy.

HIGH-TEMPERATURE GETTERS FOR ELECTRONIC TUBES Irving E. Levy, Malden, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass, at corporation of Delaware Application September 17, 1953, Serial No. 386,815

2 Claims. (Cl. 313-174) This invention relates to electronic tubes generally, whether formed in tubular, spherical or other shape, and in particular to thermionic tubes having a hot element, usually an incandescent filament, such as a cathode or a cathode heater having a coating, usually of oxide, to improve electron emission or to serve as insulation or both.

In the manufacture of such tubes it is customary to remove residual gas by means of so-called getters which are active chemical substances, such as barium and magnesium, which combine with certain gases when heated. Sometimes the getter substances are flashed but this invention relates particularly to getters in which the substances are merely heated to temperatures below the flashing point. The invention is particularly useful in tubes which operate at high temperatures, such as the modern miniature tubes, where most substances, such as barium, degas at the high temperature. In tubes where the getter is near the hot element there is danger of injury to the aforesaid coating due to chemical reaction between the coating and the active getter material if they come into contact while hot. If the hot element be formed of certain elements such as nickel it may also alloy with zirconium to form a low-melting eutectic.

Objects of the invention are .to remove the residual gases and keep them removed at high temperatures, to provide a thermionic tube in which the getter can be closely associated with the hot element without danger of damage to its coating, and generally to improve tubes of the type referred to.

In one aspect the invention involves a tube comprisins an anode, a heated cathode, and a getter mounted on the side of the cathode opposite the anode. The cathode may be heated directly 'by passing current through it or indirectly with an adjacent heater. In the case of a tubular cathode the getter is preferably mounted inside the cathode with the anode on the outside.

In another aspect the invention comprises a getter having a core of getter material and a shield around the core, the shield being formed of material which is inert to the getter material when hot and having spaces to admit gas to the getter material. Preferably the shield is in the form of a wire helix around the core with spaces between turns to admit gas to the getter material.

In a further aspect the invention involves a tube comprising a hot element, such as a cathode or a cathode heater, and a getter juxtaposed to the hot element, the getter including a core of material which reacts with the hot element when the two come into contact, together with a shield around the core to prevent said contact, the shield being formed of material which is inert to the element and core and being disposed around the core with openings to admit gas to the core. Preferably the core comprises zirconium and the shield is in the form of a wire helix and is formed of tungsten.

" nited States Patent 2,747,124 Patented May 22, 1956 In still another aspect the invention involves a tube comprising a cathode, a heater coated with insulating material, a getter including a core of getter material which reacts with the insulating material when the two materials contact while the heater is hot, and a shield for the core, the shield being inert to both materials when hot and being fast to the cathode.

For the purpose of illustration a typical embodiment of the invention is shown in the accompanying drawings in which:

Fig. l is a longitudinal central section of a tube built according to the present invention;

Fig. 2 is an end view from line 2-2 of Fig. 1; and

Pi g. 3 is a side elevation ofthe getter.

The particular embodiment of the invention chosen for the purpose of illustration comprises a metallic envelope 1 which also serves as an anode, .a metallic base ring 2 soldered to the envelope at 3, an insulating disk 4 sealed in the ring 2, a tubular cathode 5, a cathode heater 6 and a getter comprising a core 7 and a shield 8 of wire wound spirally around the core with spaces between turns. While the heater may be any suitable type, in the illustration it is the so-called folded type. The getter is mounted on the inner side of the tubular cathode by Welding the ends of the shield Wire '8 to the cathode. The core 7 is preferably formed of zirconium and the shield wire 8 of tungsten. Zirconium will not only get and keep tube gases at temperatures above 850 C. but it is an increasingly efiective getter with increasing temperature up to 1200 C. Thus by locating a getter of this kind in close association with a hot ele ment, such as a heated cathode or cathode heater, exceptionally good results are obtained. However, when the getter is close to the hot element, it must be shielded as aforesaid to guard against accidental contact with the hot element because of its great chemical aflinity for the coating of the hot element. 'For example, when using a zirconium getter with an alumina coating, the reaction is 3Zr+2AlzO3=3ZrO2+4AL thereby producing gas and causing cathode leakage, and with a nickel cathode zirconium would alloy with it to form a low-melting eutectic if the two came into contact while hot.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. In an electronic tube, a getter structure including a core of zirconium and a shield of tungsten, an electrode element adapted to be maintained at high temperature adjacent said getter structure, said shield being interposed between said electrode element and said core and having an opening to permit access of gas within said tube to said core.

2. In an electronic tube, a getter structure including a core of zirconium and a shield of tungsten, an electrode element adapted to be maintained at high temperature adjacent said getter structure, said shield being interposed between said electrode element and said core and comprising a wire helix around said core with spaces between turns to permit access of gas within said tube to said core.

References Cited in the file of this patent UNITED STATES PATENTS 2,469,626 Beers May 10, 1949 

1. IN AN ELECTRONIC TUBE, A GETTER STRUCTURE INCLUDING A CORE OF ZIRCONIUM AND A SHIELD OF TUNGSTEN, AN ELECTRODE ELEMENT ADAPTED TO BE MAINTAINED AT HIGH TEMPERATURE ADJACENT SAID GETTER STRUCTURE, SAID SHIELD BEING INTERPOSED BETWEEN SAID ELECTRODE ELEMENT AND SAID CORE AND HAVING AN OPENING TO PERMIT ACCESS OF GAS WITHIN SAID TUBE TO SAID CORE. 